Debug race condition

["cmxu" <cmxu@rdsk.net>]

Hello:

        i try to make openbsd work in polling mode (based on liug's work on
freebsd), it works very well except ...

        When fxp0 under heavy traffic, if i run "ifconfig fxp0 up", system
crashed!  it happened in fxp_add_rfabuf -> MCLGET,
the mclfree->mcl_next suddenly changed to something like 0xa020xxxx, its a
invalidat address. It seems there's some race condition.
This is my first time try to hack openbsd kernel, maybe you guy can give me
some advise on how to debug a race condition.

Best regards

cmxu@rdsk.net